This proposal contains plans for studies on several different topics in transfer RNA research: (1) genetic and biochemical studies on the regulation of the biosynthesis of tRNA and aminoacyl-tRNA synthetases; (2) comparative studies on the structure of specific tRNA precursors from E. coli, yeast and mammalian cells; (3) the preparation and use of tRNAs with photoreactive groups; (4) biochemical analysis of nonsense suppressor tRNAs in yeast.